1. Field of the Invention
The invention relates to an illumination device having at least one LED which can be connected through circuit means to a voltage source, which is selectively formed by a battery unit or an accumulator unit, as well as an intelligent bottom unit for controlling the charge of the accumulator unit. The illumination device and the bottom unit are particularly suitable for handgrips of medical diagnostic instruments, such as a laryngoscope.
2. Description of the Background Art
DE 203 08 431 U1 discloses a handgrip for a laryngoscope having a cylindrical elongate housing made of plastics into which a light insert is inserted, which light insert has an elongate battery body of cylindrical shape. A light bulb is provided at the top side of the battery body, which light bulb protrudes into an insertion piece made of transparent material at the upper end of the housing. The light bulb is upwardly biased through biasing means and is slidable in the longitudinal direction of the battery body. A battery unit consisting of two dry batteries having 1.5 V each can be inserted in the battery body, resulting in a voltage of 3 V altogether. It is also possible to introduce an accumulator unit in the battery body, wherein the voltage of a newly charged accumulator usually amounts to 4 V.
Due to technological reasons there are limits to the brightness, i.e. the luminous flux and the illumination intensity, of the light bulbs used in the prior art. The service life of a light bulb in most cases amounts to a few hours.
A possible alternative to the light bulb is nowadays increasingly offered by the LED (light emitting diode) technology. The values for luminous flux and illumination intensity of LEDs can considerably exceed the values of light bulbs. Moreover, the service life to be expected for an LED is multiple times as high as the one of a light bulb.
In the case of LED applications presently used in most cases pre-resistors connected in series are inserted in addition to the LED and then connected to a voltage source (battery or accumulator). The brightness of the LED is thus dependent on the voltage of the battery or the accumulator and therefore fluctuates in an undesirable manner.
The LED should in principle be supplied with a constant current in order to guarantee a uniform brightness irrespective of the battery voltage. In this regard, it is conceivable to supply the LED through a current regulator with a constant current irrespective of the voltage applied.
If, however, it is desired to give a user the possibility to choose between dry batteries and accumulators, the problem arises that different ranges of operation are to be observed for the different types of voltage sources. A dry battery supplies an electronic system with fundamentally different input voltage values than, for example, a Li-ion accumulator cell.
Normally in the case of laryngoscopes two dry batteries connected in series or an accumulator cell are used as energy supply. The two dry batteries connected in series have a range of operation of 2 to 3 V, whereas the accumulators have an operating range of 3 to 4 V.
It is not possible to operate a current regulator in a universal operating range from 2 to 4 V, because this would lead to damage of the accumulators. In order to protect the accumulators, it is indispensable to operate them only up to approximately 3 V. Operating them with a voltage of 2V would lead to irreversible damage of the accumulators.
Known diagnostic instruments operated with accumulator units do neither give an indication of the charging state of the accumulator unit nor do they have any charging management to optimize the charging process. Thus the charging time is not optimized, and furthermore the user does not know whether and if so, for how long he/she can still use the diagnostic instrument until the accumulator unit has to be recharged. This is the more problematic, the older, and thus the more unreliable, an accumulator unit is.